In some image forming apparatuses, a developer for charging a toner is dismountable with respect to a toner feeding section for the sake of the maintenance on the developer and the like. Sometimes, the direction from which the developer is mounted or dismounted with respect to the toner feeding section is limited by the parts arranged around the developer. The toner feeding section feeds a toner from the opening thereof to the opening of the developer.
In such an image forming apparatus, a sponge (sealer) is arranged between the edge of the opening of the toner feeding section and that of the opening of the developer so as to seal the part between the edge of the opening of the toner feeding section and that of the opening of the developer. For example, the sponge is arranged on the edge of the opening of the developer. To be dismounted from the toner feeding section, the developer is sometimes moved towards a direction intersecting with the axis of the opening of the toner feeding section. During the process of mounting the developer on the toner feeding section, if a lateral side of the sponge is contacted with the toner feeding section, then a shear force acts on the sponge and consequentially damages the sponge. It is greatly likely that the toner leaks from the position where the sponge is damaged. If the sponge is thinned, then the shear force acting on the sponge can be reduced. However, if the sponge is thin, it is likely that the toner leaks from between the toner feeding section and the developer.